Paper mill roll



y 1961 J. J- STEVENSON ET AL 90 PAPER MILL ROLL Filed Sept. 29, 1958 GINVENTOR-f [5 B dq PAPER MILL RoLL James Joseph Stevenson and PhilipRalph Dowden, Erie, Pa, assignors to Continental Rubber Works, Erie,Pa., a corporation of Pennsylvania Filed Sept. 29, 1958, Ser. No.763,870 4 Claims. (11. 29-132 This invention is a roll for papermachines which is particularly useful as a top press roll in the presssection where the paper web is so weak and tender that it must besupported on felts which carry it through the nip of the rolls. The toppress roll is critical because it comes into direct contact with thepaper Web and must be free of any tendency to pick up the paper fibersor the web will be damaged and may even break and interrupt thecontinuous operation. Granite has been considered the best knownmaterial for top press rolls although rolls of hard rubber with graniteor rock like particles bonded therein are used. These hard rubber rollsall provide an active surface of rock which simulates the action ofgranite at lower cost and weight.

Although the roll of this invention is made of hard rubber and rockparticles, unlike the prior rolls, the rock particles are not bonded inthe rubber and fall out when the outer surface of the roll is finishground or as the outer surface wears. The resultant surface is uniformlypeppered with pits so fine as not to spoil the surface of the paperwhich act to break the water film on the roll and to provide minute ai-rcushions releasing the web from the roll. The absence of rock particlesin the surface also eliminates scoring of the doctor blade.

In the drawing, Fig. l is an elevation of a roll and Fig. 2 is anenlarged fragmentary section of the rubber covering of the roll.

The roll has the usual metal roll body 1 bonded to a hard rubber (e.g.Pusey and Jones plastorneter reading of 1 with 4; ball) covering 2 whichis finish ground to provide the paper Web contacting surface 3. Theparts so far described follow the prior :art such as Patents 1,563,943;1,537,439; 1,787,890; Re. 18,111; 2,062,317; and 2,280,208. In the priorart, as represented by these patents, granite rolls remained the best inperformance and the hard rubber rolls used were those which had anactive surface of granite or equivalent rock.

In most of the prior art hard rubber rolls, the rock particles wererelatively coarse and in all of the rolls the rock particles werebonded. Because these particles were intended to be firmly bonded in thehard rubber, they were preferably crushed or powdered so as to havejagged edges rather than having the rounded surfaces usual in sand. Inamount, the particles were at least equal to the weight of rubber andranged up to five times the weight of rubber.

In the present application, use is made of fine rock particles 4 inamount having a weight of about A; the weight of the hard rubber. Areadily available commercial rock material is natural crystal quartzgrade 1/0 having particles which will pass through a 94 mesh screen andwill be retained on a 115 mesh screen. Although these fine particles areuniformly dispersed in the hard rubber, as shown at the left in Fig. 2which shows the condition of the rubber at the end of the moldingoperation, they are not bonded to the rubber. When the roll is subjectedto the usual finish grinding operation, the particles fall out or areknocked out of the rubber surface leaving-the ground surface pepperedwith small pits.

nited States Patent ice These pits appear only where the particles havebeen eX- posed by the grinding operation. Beneath the ground surface,the particles are still embedded in the rubber and provide a solidsubsurface. The resultant active surface of the roll, instead of beingpredominantly rock, is predominantly rubber with small diameter pitswhich trap air and aid in releasing the paper web from the roll surface.Because the rock material does not form the active surface of the roll,it need not be selected for its paper releasing properties as has beenthe case in the prior hard rubber rolls. Neither the material nor itssize or shape is critical. The particles should not be so large as toprovide pits which would make the active surface of the roll too roughfor the grade of paper. It will be noted that the depth of the pits onthe active surface averages less than the diameter of the particles andthat below the active surface the rubber covering is solid andsubstantially rock hard, as shown by the plastometer reading givenabove.

Because the particles do not form any substantial part of the activesurface of the roll, the material is not critical. Silica is a readilyavailable material which might be considered preferred because of itscheapness.

For the hard rubber covering 2, butadiene copolymer elastomers arepreferred because of their oil resisting and heat resisting properties.When a roll bearing overheats, the temperature rises rapidly and theability of the hard rubber covering to stand temperatures up to 200 F.without softening or cracking is important. At these temperatures,granite rolls crack. Another advantage of the butadiene elastomers isthat they can be applied in much greater thicknesses if desired. Whileother hard rubber coatings have practically been limited to thickness of/2", the butadiene rubber can be applied in thicknesses up to 2 /2" andmore. The rubber should not bond to the rock particles although atendency to bond may be overcome by using a releasing agent which willprevent bonding. Non-wetting or water repellent properties are desirablebecause the purpose of the rolls is to remove water from the paper web.

The action of the roll on the moist paper web is better than granitewhich has heretofore been considered to have the best action. There isalmost no tendency for the paper web to stick to the surface. Anotheradvantage is that water does not form in a continuous film around theroll so as to interfere with the removal of water from the paper web.The minute pits formed by the removal of the fine particles act to breakthe water film which would otherwise follow around the roll and bereturned to the paper web. The butadiene rubber has very little tendencyto stick to paper fibers. While paper fibers drying on other rolls mustbe scraped off, scraping is not necessary with the butadiene rubber.

Not only does the roll surface have a better action on the paper web,but it does not heat or wear or score the doctor blade because there isessentially no rock in the active surface. The active surface of theroll also Wears longer before needing refinishing. When substituted forcommercial hard rubber paper rolls, the present rolls run from two tothree times as long before requiring regrinding. Wear of the activesurface does not change the action. As the surface wears, fine particleswhich had previously been embedded are exposed and fall out continuouslyrenewing the pitted surface.

The roll can be used with all kinds of paper even including ground woodpulp, which is considered one of the most diflicult to handle.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A paper machine roll comprising a roll body and a covering bonded tothe body comprising hard butadiene copolymer rubber having uniformlydispersed therein fine silica particles of substantially 100 meshunbonded to the rubber and said roll having a finish ground surface inwhich the great majority of the particles exposed by finish grindinghave fallen out so said finish ground surface is a smooth essentiallysilica free active surface with fine pits throughout promoting releaseof paper fibers while the unexposed particles remain in the rubber toprovide a hard subsurface.

2. A paper machine roll comprising a roll body and a covering bonded tothe body comprising hard rubber having uniformly dispersed therein finerock particles of substantially 100 mesh unbonded to the rubber and saidroll having a finish ground surface in which the great majority of theparticles exposed by finish grinding have fallen out so said finishground surface is a smooth essentially rock free active surface withfine pits throughout promoting release of paper fibers while theunexposed particles remain in the rubber to provide a hard subsurface.

3. A paper machine roll comprising a roll body and a covering bonded tothe body comprising hard butadiene copolymer rubber having uniformlydispersed therein fine rock particles unbonded to the rubber and saidroll having a finish ground surface in which the great majority of theparticles exposed by finish grinding have fallen out so said finishground surface is a smooth essentially rock free active surface withfine pits throughout promoting release of paper fibers while theunexposed particles remain in the rubber to provide a hard subsurface.

4. A paper machine roll comprising a roll body and a covering bonded tothe body comprising hard rubber having uniformly dispersed therein finerock particles unbonded to the rubber and said roll having a finishground surface in which the great majority of the particles exposed byfinish grinding have fallen out so said finish ground surface is asmooth essentially rock free surface with fine pits throughout promotingrelease of paper fibers while the unexposed particles remain in therubber to provide a hard subsurface.

References Cited in the file of this patent UNITED STATES PATENTS1,563,943 Adams et a1. Dec. 1, 1925 1,787,890 Woodward Jan. 6, 19312,062,317 Joseph Dec. 1, 1936 2,168,233 Millspaugh Aug. 1, 19392,280,208 Wilkie Apr. 21, 1942 2,332,514 Holtzclaw Oct. 26, 19432,569,546 Treue Oct. 2, 1951

